Radiative cooling fabric and fabrication method for the same

ABSTRACT

A fabric includes one or more yarns. Each of the one or more yarns include a plurality of filaments. Each of the filaments has an average diameter in a range of 20-50 μm such that the fabric has an infrared radiation transmittance at a wavelength of 9.5 μm of at least 37%.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. 119(e) of U.S.Provisional Application No. 62/931,727, filed Nov. 6, 2019, the contentof which is hereby incorporated in its entirety.

TECHNICAL FIELD

This disclosure is generally related to fabrics for apparels, and morespecifically to radiative cooling fabrics for apparels and methods forfabricating the same.

BACKGROUND

Problems associated with the energy crises and climate change arebecoming more critical and needs to be addressed. According to recentresearch, 15% of all electricity consumed globally is used to cool homesand offices, which in turn causes an increase of greenhouse gasemissions worldwide. Therefore, development of new technologies toreduce the energy demand is needed. For example, increasing the coolingset-point temperature by 2° C. can save over 20% of energy globally.

Personal cooling management would be an effective method to reduce theenergy cost. In a typical indoor environment, the bodies' radiative heatlost in the mid-infrared thermal radiation (wavelength range of 7 to 14μm) with a skin temperature of 33.5° C. in human body accounts for morethan 50% of the total heat lost. Most of the conventional textilefabrics like cotton and polyester fail as they are infrared radiation(IR) opaque materials.

SUMMARY

Described herein are radiative cooling fabrics and apparels made of thefabrics, and methods for fabricating the fabrics.

In one aspect, a fabric includes one or more yarns. Each of the one ormore yarns include a plurality of filaments. Each of the filaments hasan average diameter in a range of 20-50 μm such that the fabric has anIR transmittance at a wavelength of 9.5 μm of at least 37%. In someembodiments, the fabric has a stiffness of less than 50 measured bysystems from PhabrOmeter or Nu Cybertek.

In some embodiments, each of the one or more yarns has an averagediameter of at most 400 μm. In some embodiments, the one or more yarnsinclude at least one yarn having a coating on its surface. The one ormore yarns may have different colors by including dyestuff. In someembodiments, the one or more yarns include an ultraviolet block agent.In some embodiments, the ultraviolet block agent includes ZnO or TiO₂.In some embodiments, the one or more yarns include one or more ceramicfillers.

In some embodiments, the fabric has a porosity in a range of 0-12%.Porosity is defined as 1 minus cover factor in this disclosure.

In some embodiments, the filaments comprise one or more of polyethylene,polypropylene, or polyamide.

In another aspect, an apparatus includes a fabric. The fabric includesone or more yarns. Each of the one or more yarns include a plurality offilaments. Each of the filaments has an average diameter in a range of20-50 μm such that the fabric has an IR transmittance at a wavelength of9.5 μm of at least 37%. In some embodiments, the apparatus includes oneof an apparel, a footwear, a tent, or a sleeping bag.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features of various embodiments of the present technology areset forth with particularity in the appended claims. A betterunderstanding of the features and advantages of the technology will beobtained by reference to the following detailed description that setsforth illustrative embodiments, in which the principles of thedisclosure are utilized, and the accompanying drawings of which:

FIG. 1 is a schematic diagram depicting yarn fabrication apparatusaccording to one example embodiment.

FIG. 2 is a diagram showing cooling performances, fabric thicknesses,and IR transmittances of various woven fabrics.

FIG. 3 is a diagram illustrating stiffness test data and thickness dataof PE fabrics formed by the disclosed techniques, according to oneexample embodiment.

FIG. 4 is a diagram illustrating stiffness test data and thickness dataof conventional PET fabrics.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thedisclosure. However, one skilled in the art will understand that thedisclosure may be practiced without these details. Moreover, whilevarious embodiments of the disclosure are disclosed herein, manyadaptations and modifications may be made within the scope of thedisclosure in accordance with the common general knowledge of thoseskilled in this art. Such modifications include the substitution ofknown equivalents for any aspect of the disclosure in order to achievethe same result in substantially the same way.

Unless the context requires otherwise, throughout the presentspecification and claims, the word “comprise” and variations thereof,such as, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.” Recitationof numeric ranges of values throughout the specification is intended toserve as a shorthand notation of referring individually to each separatevalue falling within the range inclusive of the values defining therange, and each separate value is incorporated in the specification asit were individually recited herein. Additionally, the singular forms“a,” “an” and “the” include plural referents unless the context clearlydictates otherwise.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present disclosure. Thus, the appearances of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment, but may be in some instances. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

Various embodiments described herein are directed to IR transparentfabric for personal body cooling purposes. Prior work in the fieldproposed fabrics that are made with a fiber/filament having a diameterof about 1 μm or less to be effective for infrared transparency. It hasbeen found that fibers should be made with small diameter (e.g., a fewmicrometers or narrower) so as to allow infrared radiation from a humanbody to pass through. However, fibers of small diameters are weak fornormal textile manufacturing processes. Techniques disclosed herein usefibers with much larger diameters of at least 20 μm to make strongeryarns for the radiative cooling fabric, which significantly improves theproduction quality and rate as traditional textile materials. Further,the techniques disclosed herein provides fabrics that is infraredtransparent. For example, the disclosed fabrics have an IR transmittanceat a wavelength of 9.5 μm of at least 37%.

Embodiments will now be explained with accompanying figures. Referenceis first made to FIG. 1. FIG. 1 is a schematic diagram depicting yarnfabrication apparatus 100 according to one example embodiment. The yarnfabrication apparatus 100 includes a food hopper 102 configured toreceive polymer granules 104. The polymer granules 104 includes one ormore materials that are selected to form thin filaments for the yarn.For example, the materials may include selected polymers and otheradditives. In some embodiments, the selected polymers may include one ormore of polyethylene, polypropylene, or polyamide. In some embodiments,the selected additives may include a coloring agent, an ultraviolet (UV)block agent or other functional agents.

The yarn fabrication apparatus 100 further includes a heating unit 106that melts the polymer granules 104 at a predetermined elevatedtemperature to generate a polymer melt 108. The polymers used in makingpolymer yarn may include, for example, linear low-density PE (LLDPE) orhigh-density PE (HDPE) with a viscosity in the range of 17-30 g/10 min(based on ASTM D1238), which provides moderate mobility in followingmelt extrusion process. A pump 110 is employed to move the polymer melt108 to a spinneret apparatus 112 that includes a plurality of spinnerets112-1. Each of the spinneret 112-1 extrudes/produces a filament/fiber114 that is collected by a yarn driving roller 116. Depending on anumber of spinnerets 112-1 in the spinneret apparatus and a materialflow rate, different filament sizes with various filament numbers may beobtained. In some embodiments, an average diameter of the filaments 114is controlled to be in a range of 20-50 μm. In some embodiments, to forma cooling fabric that has a nice skin touch, the average diameter of thefilaments 114 is controlled in a range of 25-50 μm, 30-50 μm, 35-50 μm,40-50 μm, 20-45 μm, 25-45 μm, 30-45 μm, 35-45 μm, 20-40 μm, 25-40 μm,30-40 μm, 20-35 μm, 25-35 μm, or 20-30 μm.

While the filaments 114 are pulled by the yarn driving roller 116, thefilaments 114 are cooled by air 118. In some embodiments, alternativelyor additionally, after the filaments 114 are cooled, they may be subjectto steam treatment 120 to modify its property. In some embodiments, theas-spun multi-filament yarn is drawn from the spinnerets 112-1 with adraw ratio of at least 2.2:1 and twisted at least 155/m to form a strongyarn. The drawing process increases mechanical strength, e.g., tenacityand elongation, of a polymer yarn 122. For example, a drawn PE yarn mayhave a tenacity of at least 1.61 g/d and elongation of at most 111.26%.The filaments 114 are collected by the yarn driving roller 116 to formthe yarn 122, which is fed to feed roller 124. Then the yarn 122 isrolled on a bobbin 126 and ready for making a fibric.

One or more yarns 122 are made into a fabric for personal coolinggarment by weaving and knitting techniques. In some embodiments,reduction of the fabric thickness and control of the fiber/filament andyarn size may have significant effects on the cooling performance ofgarment as both of the fiber and yarn sizes affect IR transmittance.Particularly, it has been discovered that the fiber size of a yarnshould have a diameter of about 1 μm to be effective for acceptable IRtransmittance. However, using the techniques disclosed herein, the fibersize of the yarn 122 is controlled to be in the range of 20-50 μm, about20 to 50 times larger than the fiber size in the prior work of the fieldfor cooling garment. The disclosed techniques include selection ofpolymer materials, the size of the fiber, and the size of the yarn forforming a fabric that is strong and IR transparent. For example, one ormore polyethylene, polypropylene, or polyamide are employed for thematerial that can achieve acceptable IR transmittance for the fibershaving a diameter in the range of 20-50 μm, 25-50 μm, 30-50 μm, 35-50μm, 40-50 μm, 20-45 μm, 25-45 μm, 30-45 μm, 35-45 μm, 20-40 μm, 25-40μm, 30-40 μm, 20-35 μm, 25-35 μm, or 20-30 μm.

To be effective for IR transmission, a diameter of the yarn 122 iscontrolled to be at most 400 μm. In some embodiments, a diameter of theyarn 122 is at most 350 μm, 300 μm, 250 μm, or 200 μm. In someembodiments, a diameter of the yarn 122 is in the range of 200-400 μm,200-350 μm, 200-300 μm, 200-250 μm, 250-400 μm, 250-350 μm, 250-300 μm,300-400 μm, 300-350 μm, or 350-400 μm.

These discoveries allow a fabric to have IR transmittance at awavelength of 9.5 μm of at least 37%. In some embodiments, a fabricformed by the techniques disclosed herein may have IR transmittance at awavelength of 9.5 μm of at least 38%, 40%, 42%, 45%, or 50%. In someembodiments, a fabric formed by the techniques disclosed herein may haveIR transmittance at a wavelength of 9.5 μm in the range of 37-50%,37-45%, 37-40%, 38-50%, 38-45%, 40-50%, 40-45%, or 45-50%.

In some embodiments, the weaving and knitting process to form thefabrics may result in pores in the fabric structure. For example, thefabrics may have a porosity in a range of 0-12%. The pores may be usedto modify the characteristics of the fabric, including IR transmittanceand air permeability.

In some embodiments, the yarn may be formed with various coloring agentsto provide colors to the yarns for creating patterns or colors on afabric. In some embodiments, the yarns may be formed with otherfunctional agents. For example, one or more UV-block agents may be addedto the yarn to give the yarn the ability to provide a better UV-blockfunction. In some embodiments, the UV-block agent may include ZnO andTiO₂. In some embodiments, the functions agents may be added to the yarnin the form of ceramic fillers. In some embodiments, the addedfunctional agents is added at most to the point that the IRtransmittance (at a wavelength of 9.5 μm) drop of the fabric does notexceed beyond 15%.

FIG. 2 is a diagram showing cooling performances, fabric thicknesses,and IR transmittances of various fabrics. First, FIG. 2 indicates thecooling performance of two woven PE fabric samples formed with thetechniques disclosed herein compared with traditional polyester andcotton woven fabric samples. The results indicated that the PE fabric(150D (denier)/24F (filament count per yarn), yarn diameter of 285 μm,filament diameter of 37 μm) with a thickness of 0.28 mm is 2.1 and 1.9°C. cooler than conventional PET woven fabric (0.29 mm in thickness) andcotton broadcloth fabric (0.27 mm in thickness), respectively in skintemperatures; while the PE fabric (150D/50F yarn diameter of 285 μm,filament diameter of 22 μm) with a thickness of 0.36 mm was 1.8 and 1.6°C. cooler than the PET woven fabric and the cotton broadcloth fabric,respectively in skin temperatures. Further, The IR transmittance is 50%,37%, 0%, and 0% for the 150D/24F PE fabric, the 150D/50F PE fabric, thePET woven fabric, and cotton broadcloth fabric, respectively. Theseresults demonstrate the advantages of the disclosed PE fabrics inthermal regulation.

In some embodiments, the fabrics formed by the techniques disclosedherein may have stiffness less than 50. FIG. 3 is a diagram illustratingstiffness test and thickness data of PE fabrics formed by the disclosedtechniques, according to one example embodiment. FIG. 4 is a diagramillustrating stiffness test and thickness data of conventional PETfabrics. The stiffness test is conducted based on American Associationof Textile Chemists and Colorists (AATCC) TM202 standard.

As shown in FIG. 3, the woven fabric made of 150D/24F PE yarn (yarndiameter of 285 μm; filament diameter of 37 μm) having 0.26 mm inthickness has a stiffness of 42.55 while the woven fabric made from500D/72F PE yarn (yarn size of 376 μm; filament diameter of 37 μm)having 0.53 mm in thickness has a stiffness of 49. The woven fabric madeof 150D/24F PE yarn has a softer touch than that of the woven fabricmade from 500D/72F PE yarn. The results indicate the additional benefitsof controlling the yarn diameter to be at most 400 μm in apparelapplications as smaller yarn size contributes to thinner fabrics withbetter drapability.

As shown in FIG. 4, woven PET fabric sample 1 (0.38 mm in thickness)with a filament diameter of 36 μm has a stiffness of 56.64 while wovenPET fabric sample 2 (0.41 mm in thickness) with 15 μm filament diameterhas a stiffness of 44.24. For the conventional fabric, the filamentdiameter needs to be below 20 μm (15 μm in this example) to obtain theacceptable skin touch (less than 50 in stiffness). Referring back toFIG. 3, the fabrics made from the techniques disclosed herein canachieve the acceptable stiffness even with a filament diameter of 37 μm.

In summary, the fabrics consistent with this disclosure achieve goodinfrared-transmittance, good cooling performance, and good drapeabilitywhich makes them appropriate for apparel applications. The fabrics canalso be employed in other fields that need cooling fabrics.

In one aspect, a disclosed radiative cooling fabric has an IRtransmittance at a wavelength of 9.5 μm of at least 37%, e.g., fromtransmittance data collected from a thermal camera.

In another aspect, the fabrics may be made from material which has atransmittance of infrared radiation at a wavelength of 9.5 μm of atleast 38%. The materials may include, but not limited to, polyethylene,polypropylene, and polyamide.

In yet another aspect, the fabrics are made from a yarn with filamentshaving an average diameter in the range of 20-50 μm. The yarn has anaverage diameter of at most 400 μm.

In yet another aspect, a radiative cooling fabric made by drawn PE yarnshas thickness of at most 400 μm with porosity range of 0-12%.

In yet another aspect, the yarn may be coated with sizing materialbefore weaving or knitting to avoid the statics, enhance strength, andimprove bonding of the filaments.

The foregoing description of the present disclosure has been providedfor the purposes of illustration and description. It is not intended tobe exhaustive or to limit the disclosure to the precise forms disclosed.The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments. Many modifications andvariations will be apparent to the practitioner skilled in the art. Themodifications and variations include any relevant combination of thedisclosed features. The embodiments were chosen and described in orderto best explain the principles of the disclosure and its practicalapplication, thereby enabling others skilled in the art to understandthe disclosure for various embodiments and with various modificationsthat are suited to the particular use contemplated. It is intended thatthe scope of the disclosure be defined by the following claims and theirequivalence.

What is claimed is:
 1. A fabric comprising: one or more yarns, each ofthe one or more yarns including a plurality of filaments, wherein eachof the filaments has an average diameter in a range of 20-50 μm suchthat the fabric has an infrared radiation (IR) transmittance at awavelength of 9.5 μm of at least 37%.
 2. The fabric of claim 1, whereinthe filaments has an average diameter in a range of 20-40 μm.
 3. Thefabric of claim 1, wherein the filaments comprise one or more ofpolyethylene, polypropylene, or polyamide.
 4. The fabric of claim 1,wherein the fabric has a porosity in a range of 0-12%.
 5. The fabric ofclaim 1, wherein the one or more yarns include at least one yarn havinga coating on its surface.
 6. The fabric of claim 1, wherein the one ormore yarns contain dyestuff.
 7. The fabric of claim 1, wherein the oneor more yarns include an ultraviolet block agent.
 8. The fabric of claim7, wherein the ultraviolet block agent includes one or more of ZnO orTiO₂.
 9. The fabric of claim 1, wherein the one or more yarns includeceramic filler.
 10. The fabric of claim 1, wherein each of the one ormore yarns has an average diameter of at most 400 μm.
 11. An apparatuscomprising a fabric, wherein the fabric comprises: one or more yarns,each of the one or more yarns including a plurality of filaments,wherein each of the filaments has an average diameter in a range of20-50 μm such that the fabric has an infrared radiation (IR)transmittance at a wavelength of 9.5 μm of at least 37%.
 12. Theapparatus of claim 11, wherein the filaments has an average diameter ina range of 20-40 μm.
 13. The apparatus of claim 11, wherein thefilaments comprise one or more of polyethylene, polypropylene, orpolyamide.
 14. The apparatus of claim 11, wherein the fabric has aporosity in a range of 0-12%.
 15. The apparatus of claim 11, wherein theone or more yarns include at least one yarn having a coating on itssurface.
 16. The apparatus of claim 11, wherein the one or more yarnscontain dyestuff.
 17. The apparatus of claim 11, wherein the one or moreyarns include an ultraviolet block agent.
 18. The apparatus of claim 17,wherein the ultraviolet block agent includes one or more of ZnO or TiO₂.19. The apparatus of claim 11, wherein the one or more yarns includeceramic filler.
 20. The apparatus of claim 11, wherein each of the oneor more yarns has an average diameter of at most 400 μm.